A transmission provides different gear ratios between the engine and drive wheels of a typical land vehicle. The transmission enables the vehicle to accelerate from rest up to a maximum speed through a wide speed range while the engine operates efficiently. In most applications, the transmission is positioned in the vehicle power train between the engine and the propeller shaft. The engine's power flows through the transmission and propeller shaft and is delivered to the differential and drive axles.
Most vehicle transmissions operate within a preset range of gear ratios. While this is not a problem for passenger cars used for commuting and the like, it can be a problem for special purpose vehicles, such as pickup trucks, used for carrying or towing heavy loads. Excessive engine and transmission wear, fuel consumption, and operating costs can result from gear ratios that are set too high at the time of their manufacture. A need, therefore, exists for an "add-on" assembly which can be easily and economically inserted into the power train of a vehicle for reducing the gear ratio between the engine and drive axles.